This invention relates generally to turbo-machinery, and in particular to a multi-stage supercharger arrangement with cross flow between compression stages.
Emissions regulations and market forces have continually driven engine manufacturers toward higher engine output, smaller overall size, and cleaner operation. Currently designers of state of the art internal combustion engines concentrate on the few tools still available to meet these challenges. A current area of focus for engine designers is the engine air system, and, more particularly, the combustion engine""s turbomachinery or turbochargers.
State of the art combustion systems require the engine""s air and fuel to be delivered to the combustion chamber at increasingly higher pressure and higher mass flow. With the desire to provide higher combustion air pressure (i.e., xe2x80x9cboostxe2x80x9d pressure), engine manufacturers have used series turbocharger arrangements. These arrangements dispose two separate turbocharger assemblies on the engine, each having a compressor driven by its own turbine and designed to provide a predetermined portion of the overall required pressure ratio with the output of one turbocharger assembly (first stage) feeding the input of the other turbocharger assembly (second stage). Such arrangements allow each turbocharger assembly to be individually optimized for best performance. Often, the engine may have more than one series turbocharger arrangement adapted to deliver air to some subset of combustion cylinders. Cooling the partially compressed air between the first and second stage further improves efficiency.
Another turbocharger arrangement is the twin compressor turbocharger (xe2x80x9cTCTxe2x80x9d). U.S. Pat. No. 5,157,924 discloses an example of a turbocharging system that employs the TCT arrangement. An important feature of the TCT arrangement is the mounting of two compressor wheels (first and second stage wheels) on a common rotor shaft. Ducting internal to the device routes the partially compressed air output from the first stage wheel to the inlet of the second stage wheel. TCTs have fewer rotor assemblies on the engine compared with a series turbocharger arrangement and reduce bearing and shaft losses.
Similar with series turbocharger arrangements, TCTs may also have inter-stage cooling. One manner of inter-stage cooling uses a generally annular cooler disposed about the rotor shaft. The overall layout of the air flow passageways directing air into the annular cooler, as well as toward the second stage compressor inlet generally requires a larger package for the rotor housing. Where the mass flow and pressure performance characteristics of the compressor and turbine wheels increase with the square of rotor speed and diameter, thermal heat transfer considerations increase directly (i.e., linearly) with increased mass flow. The mismatch of square turbo performance and linear heat transfer effects makes inter-stage cooled TCTs an essentially non-scalable, turbo-machinery device. Large mass flow and high-pressure applications for TCT technology result in moderate diameter wheels but very large cooler sizes, and, consequently, a very large outside diameter of the rotor housing.
The cooler also generally dictates the axial length of the TCT""s compressor section. The overall efficiency of a series turbocharger arrangement is strongly dependent on incurring little or no losses in pressure in the inter-stage ducting. This efficiency requirement drives design of a very low pressure-drop cooler core. The low pressure-drop cooler core in turn requires slowing the airflow down to minimum velocity over the largest possible area (longest axial length, largest outside diameter).
Additionally, measured against traditional inter-stage cooled series turbocharger arrangements, the inter-stage cooled TCT device generally can devote less space and length to smoothly transition the inter-stage airflow, since the air must flow from the first stage compressor outlet, through the cooler, and toward the second stage inlet. The resulting small airflow cross sections, sharp turning radii, and abrupt expansions and contractions significantly decrease the inter-stage cooled TCT""s efficiency.
Moreover, balancing the diameter, length, and airflow ducting requirements noted above, generally results in the designer reducing the amount of cooler heat transfer capability of the TCT machine and increasing the interstate cooled temperature fed into the second stage inlet. This increase in interstate temperature again decreases the TCT""s efficiency.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, a supercharger arrangement includes a first rotor assembly, including a first compressor, having a first compressor inlet and a first compressor outlet. A second compressor has a second compressor inlet and a second compressor outlet. A second rotor assembly includes a third compressor, having a third compressor inlet and a third compressor outlet, and a fourth compressor, having a fourth compressor inlet and a fourth compressor outlet. A first inter-stage conduit connects the first compressor outlet and the fourth compressor inlet.
According to another aspect of the invention, a supercharged engine has a combustion chamber. An intake conduit is connected with the combustion chamber. Also, an exhaust conduit connects with the combustion chamber. The supercharged engine includes supercharger arrangement having a first rotor assembly, including a first compressor and a second compressor. A second rotor assembly includes a third compressor and a fourth compressor. An inter-stage conduit connects an outlet of the first compressor with an inlet of the fourth compressor.
According to yet another aspect of the present invention, a method of compressing gas is provided, including compressing a first gas to a first compression stage using a first compressor wheel; further compressing the first gas to a second compression stage using a fourth compressor wheel; compressing a second gas to the first compression stage using a third compressor wheel; and further compressing the second gas to the second compression stage using a second compressor wheel.